1. Field of the Invention
The present disclosure relates to a fuel cell.
2. Discussion of the Background
In general, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane formed as a polymer ion exchange membrane. In the fuel cell, a membrane electrode assembly (MEA) is sandwiched between separators (bipolar plates), the membrane electrode assembly being formed by disposing an anode electrode and a cathode electrode on respective sides of the solid polymer electrolyte membrane, each electrode including a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon). The fuel cell is used, for example, as an in-vehicle fuel cell stack which is obtained by stacking a predetermined number of unit cells.
In a membrane electrode assembly of this type, a so-called stepped MEA may be formed in such a manner that one gas diffusion layer is set to have a surface area smaller than that of the solid polymer electrolyte membrane, while the other gas diffusion layer is set to have a surface area equal to that of the solid polymer electrolyte membrane.
Normally, a large number of membrane electrode assemblies are stacked in a fuel cell stack, and it is desired that the membrane electrode assemblies be produced inexpensively in order to reduce production costs. Consequently, various proposals have been made to simplify the configuration, while reducing the amount of expensive solid polymer electrolyte membrane in use.
For example, the membrane electrode assembly disclosed in Japanese Unexamined Patent Application Publication No. 2008-41337 includes a membrane electrode assembled body 4 which, as illustrated in FIG. 6, has a polymer electrolyte membrane 1, a first electrode layer 2a disposed on one side of the electrolyte membrane 1, a first gas diffusion layer 3a disposed on the side of the first electrode layer 2a opposite to which the electrolyte membrane 1 is disposed, a second electrode layer 2b disposed on the other side of the electrolyte membrane 1, and a second gas diffusion layer 3b disposed on the side of the second electrode layer 2b opposite to which the electrolyte membrane 1 is disposed. The membrane electrode assembled body 4 is provided with a resin frame 5 so as to surround the lateral side of the electrolyte membrane 1 which includes the entire outer periphery of the electrolyte membrane 1 and at least part of the outer periphery of the first gas diffusion layer 3a and the second gas diffusion layer 3b. 
The first gas diffusion layer 3a and the first electrode layer 2a are disposed on the surface of the electrolyte membrane 1 in such a manner that the entire outer periphery of the first gas diffusion layer 3a falls within the range of the outer periphery of the electrolyte membrane 1, and a surface area of the electrolyte membrane 1 is disposed between the outer periphery of the first electrode layer 2a and the outer periphery of the electrolyte membrane 1, along the entire outer periphery of the first electrode layer 2a. 
The second gas diffusion layer 3b extends to at least part of an area opposite to the surface area along the entire outer periphery of the electrolyte membrane 1, and the resin frame 5 is fixed to at least part of the surface area.